Method of determining mechanical parameters of an electric switching device

ABSTRACT

A method for determining mechanical parameters of an electric switching device exposed to environmental influences in which a measuring transmitter is provided for detecting the speed of a component of the drive means of the switch device at at least two consecutive times. In the case of vacuum power switches, the time of contact of the switch members and the time of the latching in the switched-on condition are preferably considered. If measurement values from comparative measurements of a given number of switches are available, the maximum intensity of a given environmental influence at which test sample can reliably operate is determined from a measurement of a test sample under normal environmental conditions.

BACKGROUND OF THE INVENTION

The present invention relates to a method for determining mechanicalparameters of an electric switching device exposed to environmentalinfluences. The electric switching device has at least one energystorage device for preparing for a switch movement for switching-on, atleast one switch chamber having switch contacts, a contact-force springadapted to be cocked by the energy storage device upon the switching-on,and a drive device for transmitting a switch movement to the switchchamber.

Known methods of the above-mentioned type, such as methods used in theproduct testing departments of the electrical industry, serve to examinethe manner of operation of the switching devices under the influence ofthe environment, thereby obtaining information as to whether theswitching device is suitable for its intended use. Such investigationsare important, in particular for the power switches of power engineeringsince the reliability of the general power supply depends upon theproper operation of such power switches. Influences of the environmentsuch as air pressure, temperature, dirt, and similar influences can varywithin wide limits and can affect the mechanical and/or electricalswitching capability of an electric switch.

The object of the present invention is to develop a method of the abovementioned type which uses a simple test, carried out after themanufacture of a switching device, to predict whether the switchingdevice is suitable for a given intended use.

SUMMARY OF THE INVENTION

The method of the present invention achieves this object by thefollowing steps:

providing a component of the drive device, which participates in theentire drive movement, with a measuring device for determining the speedof the component;

imposing a selected environmental influence with a given intensity onthe switching device;

determining the dependence of the speed of the component on time; and

repeating the measurement at different intensities of the selectedenvironmental influence.

If a number of switching devices are examined by this method, it will behighly probable that a distribution of certain properties will bedetected. This distribution is unavoidable even in instances of carefulmanufacture. For instance, variations in the energy content of springstorages, variations in the viscosity of lubricants, differences in thefriction of bearings and similar phenomena as a function of thedifferent intensity of an environmental influence will be detected. Allof these influences affect the speed of operation of the drive means ofthe switching device. For instance, the speed towards the end of theswitching-on movement can be used as a criterion for the evaluation. Ifthe speed is not sufficiently great, then a latching, necessary tomaintain the switched-on condition, does not take place and theswitching device returns entirely or partly into the switched-offcondition.

In accordance with one embodiment of the present invention, determiningthe speed of the moving component of the drive device at a large numberof times is not necessary. Rather, comparing the speeds measured duringa switching process at least two successive times during the movement ofthe component and repeating this step for all measurements issufficient.

Despite limiting the number of measurements to two points in time, ahigh degree of certainty as to the behavior of the drive means can beobtained in accordance with a further development of the presentinvention by the following steps:

determining the speed of the component at the time when the switchcontacts of the switch chamber contact each other in the course of theswitching movement; and

determining the speed of the component at the time when the switched-onposition is latched, thereby securing it. In this way, whethersufficient residual energy is still available towards the end of theswitching-on process to latch the drive means with the switch contactsof the switching device properly closed can be predicted.

Based on the method steps explained above, currently manufacturedswitching devices can be tested by measuring them with a normal value ofthe selected environmental influence. Further, to obtain the permissiblerange of use of the switching device, the values ascertained arecompared with reference values obtained from measurements with variablevalues of the environmental influence selected.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 diagrammatically illustrates a vacuum power switch as example ofswitching devices to be examined.

FIG. 2 is a block diagram illustrating the procedure of the presentinvention upon obtaining measurement values for the properties ofswitching devices.

FIG. 3 is a block diagram illustrating the procedure of the presentinvention upon testing a switching device taken from currentmanufacture.

FIG. 4 is a graph showing the dependence of the energy of the drivemeans of a switching device as a function of a given environmentalinfluence.

FIG. 5 is a diagram showing the angle of rotation of the switch shaft asa function of time.

DETAILED DESCRIPTION

FIG. 1 shows, as example of a type of switching device to be examined, avacuum power switch such as used in the voltage range of about 6 to 36kV and for rated disconnect currents of up to about 50,000 A. The maincomponents of such a power switch include a vacuum switch tube 1 havinga stationary connection stud 2, a movable connection stud 3, connectingrails 4 connected to the connection studs 2 and 3, and a drive means 5.The drive means 5 contains an "on" spring 6 and a switch shaft 7 whichreceives the energy of the "on" spring 6 and mechanically transfers theenergy to one or more vacuum switch tubes 1. FIG. 1 shows the "off"position of the power switch in which the switch shaft 7 is locked by an"on" pawl 10. If the "on" pawl 10 is released, the rotation of theswitch shaft 7, which then commences, is transmitted, via a levermechanism 12, to the movable connection stud 3 of the vacuum switch tube1 for switching-on (i.e., for closing the switch). In the levermechanism 12 shown, a contact-force spring 13, cocked during the courseof the switching-on movement, is inserted to maintain a predeterminedcontact force between the switch contacts of the vacuum switch tube 1.

In FIG. 1, arrows E1, E2, E3 and En indicate various environmentalfactors which act on the power switch and influence its manner ofoperation. One possible result of such influences is that a disconnectpawl 11, indicated in FIG. 1, which cooperates with the switch shaft 7,cannot function properly. As a result of such a malfunction, the "on"position of the power switch is not completely reached.

To carry out the method of the present invention, which will beexplained in further detail below, the power switch 1 is provided, inaccordance with FIG. 1, with a measuring device 14. The measuring device14 permits the speed of the switch shaft 7 to be determined. Themeasuring device 14 can, for example, comprise an inductive displacementpick-up such as those customary in electrical engineering product testdepartments.

FIG. 2 shows that a plurality of power switches bearing the symbols S1,S2, S3, S4 and Sn are available. The number, n, of power switches to beexamined can be any number desired, but should not be too small toobtain sufficiently reliable results. The power switches S1 to Sn areexposed to environmental influences which are caused to act, in eachcase, with different intensity. In FIG. 2, it is assumed that a givenenvironmental influence E1, which may, for instance, be the air pressureor the temperature, is caused to act in different intensities I1, I2,I3, I4 and In. The designation In indicating that the entire possiblespectrum of intensities is available with a desired or necessary finegradation. The power switches S1 to Sn are now examined with measuringdevices associated with them (corresponding to the measuring device 14in FIG. 1). Measured values for the speed as a function of the time (t),the nature of the environmental influence (E), and the intensity of thisenvironmental influence (I) are obtained as the test results. From thesemeasured values for the speed (which are provided with the simplifieddesignation v(t, E, I) in FIG. 2), values for the switch energy P(namely corresponding to the simplified designation P(E, I) in theright-hand block of FIG. 2) as a function of the nature of theenvironmental influence and its intensity can be obtained by calculationor comparative association.

After a sufficient number of measured values for the speed at differenttimes and a corresponding number of measured values for the energy ofthe drive at different times and also as a function of the nature of theenvironmental influence and its intensity are obtained, the examinationof a currently manufactured power switch merely requires a measuring andevaluating process which is easy to carry out. For this, FIG. 3 shows apower switch Sp (corresponding to FIG. 1) with a measuring device 14.The measuring device 14 is adapted, in particular, to detect the speedof rotation of the switch shaft 7 at a time t1 and at a further time t2.The time t1 corresponds to the time of contact of the switch contacts ofthe vacuum switch tube 1 during the course of the switching-on processand the time t2 corresponds to the time of the engagement of thedisconnect pawl 11. By comparing the previously obtained measuredvalues, the maximum intensity of a given environmental influence atwhich the power switch Sp can still be used can directly be determined.

As example of an evaluation, FIG. 3 shows that the power switch Sp isdependable in operation up to the intensity 14 of the environmentalinfluence E1.

FIG. 4 shows the energy balance of a power switch of the above type as afunction of the temperature as example for one of the environmentalinfluences which occur. In the graph, the switch energy is plotted overthe temperature range. Low temperatures are marked "--" and highertemperatures are marked "++". "-", "0" and "+" are intermediate values.In the upper part of the graph, a straight line has been entered aslimit line for the available energy supply.

Furthermore, in the lower part of the graph, the minimum required switchenergy is also shown in the form of a straight line. The dependence ofthe internal friction of the power switch in question on the temperatureis shown by a curve which drops from the left to the right. The residualenergy in the drive of the power switch, which differs as a function ofthe temperature, is indicated by an arrow bearing the designation PRbetween the curve and a reference line parallel to the temperature axis.The limit for the range of use of the power switch is obviously reachedat the point where the residual energy assumes the value, "0".

In FIG. 5, the angle of rotation of the switch shaft 7 of a power switchin accordance with FIG. 1 is plotted as a function of the time. Thecurve shown in FIG. 5 passes, at the time t2, above a reference linedrawn parallel to the time axis and approaches this line afterovershooting it one or more times. The exceeding of the reference linein this connection characterizes the moment that the disconnect pawl 11in FIG. 1 engages. If sufficient energy were not present at this time,the latching would not be effective and the power switch would notdefinitely reach its "on" position.

The time t1, which characterizes the time of contact of the switchcontacts of the vacuum switch tube 1 upon switching-on, is also shown inFIG. 5. By determining only these two times t1 and t2, frictionmeasurement values, which are applicable for a given type of powerswitch, can be obtained by the method in accordance with FIG. 2, thesevalues being available for comparison upon the testing of a power switchtaken from manufacture in accordance with FIG. 3. In this way, thepermissible field of use of a power switch can be easily determined.

The use of the present invention is not limited to vacuum powerswitches, but can also be used, without any basic change, in switchingdevices with switch chambers of other types for instance with sulfurhexafluoride or some other extinguishing gas. Similarly, the methoddescribed is suitable for the examining of power switches having drivemeans which, in the place of springs, contain other energy storagedevices, for instance hydraulic or pneumatic storage devices.

We claim:
 1. A method of determining mechanical parameters of anelectric switching device which is to be exposed to environmentalinfluences and which has at least one energy storage device thatprepares for a switch movement for switching-on, at least one switchchamber having switch contacts, a contact-force spring adapted to becocked by the energy storage device upon the switching-on, and a drivedevice, said drive device transmits a switch movement to the switchchamber, comprising steps of:a) providing a measuring transmitter todetermine a speed of a component of the drive device that participatesin an entire drive movement; b) imposing a selected environmentalinfluence on the switching device with a given intensity; c) determiningthe speed of the component as a function of time; and d) repeating themeasurement of steps a) through c) with different intensities of theenvironmental influence.
 2. The method of claim 1 further comprisingsteps of:e) comparing at least two speeds measured during a switchingprocess at least two successive times during the movement of thecomponent with each other; and f) repeating the comparing in step (e)for all measurements.
 3. The method of claim 2 further comprising stepsof:g) determining the speed of the component at a time that the switchcontacts of the switch chamber contact each other during a course of theswitch movement; and h) determining the speed of the component at a timethat a latching, which secures the "on" position, is active.
 4. Themethod of claim 1 further comprising steps of:e) subjecting a switchingdevice from current manufacture to a measurement at a normal value ofthe selected environmental influence; and f) comparing said normalvalues obtained in step (e) with reference values from measurements withvariable values of the selected environmental influence to obtain apermissible field of use of the switching device.
 5. A method fordetermining mechanical parameters of an electric switching device whichis to be exposed to environmental influences and which has an energystorage device that initiates a switch movement for closing the switch,a switch chamber having switch contacts, a contact-force spring adaptedto be cocked by the energy storage device upon the initiation of theswitch closing, a drive device, said drive device transmits the switchmovement to the switch chamber, and a latch, said latch secures theswitch in the closed position, comprising steps of:a) providing ameasuring device for measuring an angular rotation and an angularvelocity of the drive device; b) applying an environmental factor, at anumber n of intensities to n electric switch devices; c) repeating saidapplying step (b) for different environmental factors; d) obtaining aswitch velocity at a particular time for each intensity of eachenvironmental factor with the measuring device; and e) determining aswitch power for each intensity of each environmental factor based onthe switch velocities obtained in step (d).
 6. A method for determiningmechanical parameters of an electric switching device which is to beexposed to environmental influences and which has an energy storagedevice that initiates a switch movement for closing the switch, a switchchamber having switch contacts, a contact-force spring adapted to becocked by the energy storage device upon the initiation of the switchclosing, a drive device, said drive device transmits the switch movementto the switch chamber, and a latch, said latch secures the switch in theclosed position, comprising steps of:a) providing a measuring device formeasuring an angular rotation and angular velocity of the drive device;b) applying an environmental factor, at a number n of intensities to thenumber n of electric switch devices; c) obtaining a switch velocity at afirst time and at a second time for each intensity of the environmentalfactor with the measuring device; and d) comparing a switch power foreach intensity of the environmental factor based on the switchvelocities obtained in step (c) with a measurement of switch undernormal environmental conditions; and e) determining the maximumintensity of the environmental influence at which the switch canreliably operate based on the comparison of step (d).
 7. The method ofclaim 6 wherein the first time is a time of contact of the switchmembers and the second time is a time of latching the switch closed.